Fire retardant compositions



United States Patent 3,409,550 FIRE RETARDANT COMPOSITIONS Lincoln E.Gould, Belvedere, Califi, assignor to Shell Oil Company, New York, N.Y.,a corporation of Delaware No Drawing. Filed Dec. 30, 1965, Ser. No.517,833 10 Claims. (Cl. 252--8.1)

ABSTRACT OF THE DISCLOSURE The corrosivity of liquid fire-retardantcompositions is reduced by using an aqueous mixture of ammonium sulfateand diammonium phosphate in a weight ratio of sulfate to phosphate offrom about 1:1 to about 5:1, said mixture having a pH of between about6.5 and about 7.5.

This invention relates to improved fire extinguishing compositions. Moreparticularly, it relates to inorganic fire retardant compositionscharacterized by fire extinguishing effectiveness combined with reducedcorrosivity.

BACKGROUND The use of inorganic fire extinguishing compositions is wellknown. For some years the U.S. Forest Service and other state andfederal conservation agencies have been using as fire fighting chemicalssuch salts as diammonium phosphate, ammonium sulfate, sodium calicumborate and sodium carbonate. These compounds, alone or in variousmixtures, have been used as solids, or in various liquid or solutionforms. Currently, the most advantageous way to use formulations of thesechemicals for fighting forest fires is to drop them from aircraft. Bothfixed-wing and helicopter aircraft are employed for airdroppingfire-fighting chemicals. The chemicals are generally air-dropped ontounburned forest ahead of a fire, to serve as fire retardants, preventingthe fires further spread.

Aqueous solutions of the chemicals noted above have been found to beextremely effective for aerial fire fighting. In practice, suchsolutions are made up at airports or air strips, pumped into tanks onaircraft, and dropped from the aircraft onto fires as conditionsrequire. It has been found, however, that the aqueous solutions areextremely corrosive to many of the metals they encounter in use. Inparticular, they have been found to seriously corrode aluminum, copperand bronze, all metals used in aircraft construction. Corrosion damageto fire-fighting aircraft, caused by the solutions dropped, has become aserious economic and safety problem.

Salt solution splashed or drifted onto aluminum fuselage and controlsurfaces has been observed to etch holes in these surfaces. Solutionwhich has splashed on copper or bronze bearings has seriously corrodedthe bearings, impairing their operation. Aluminum tanks and pipes inwhich the solutions are made and stored have become breached orcorroded. As a consequence, a need has arisen for an effective aqueousfire retardant composition which is non-corrosive toward aluminum,copper, bronze and other structural metals, without losing itsfire-fighting effectiveness.

OBJECTS It is an object of this invention to provide an effectivefire-retardant composition of low corrosivity toward metals. Anotherobject of the invention is the provision of a low-cost relativelynon-corrosive mixture of fireretardant chemicals. Still another objectis the provision of a fire-retardant composition containing a particularmixture of diammonium phosphate and ammonium sulfate. A method offighting fires with such compositions is another object of theinvention, Other objects of the 3,409,550 Patented Nov. 5, 1968invention will be apparent from the following detailed description ofthe compositions thereof.

STATEMENT These objects are accomplished by the first-retardantcomposition comprising an aqueous gel, said gel comprising essentiallyas the fire extinguishing ingredients a dissolved mixture of ammoniumsulfate and diammonium phosphate wherein the weight ratio of saidsulfate to said phosphate is from about 1:1 to about 5: 1, and saidaqueous gel has a pH between about 6.5 and about 7.5, and a viscosity ofat least 1000 centipoises.

The fire retardant compositions of the invention may be prepared in anyconvenient way. For example, the ammonium sulfate and the diammoniumphosphate may be conveniently premixed in the desired proportions, andthe resulting mixture dissolved in water prior to use. Alternatively,the ammonium sulfate and diammonium phosphate may be separatelydissolved in the Water in the desired proportions.

The concentration of the inorganic mixture in the aqueous vehicle mayvary over a wide range, depending, in part, on the economics involved.It is desirable to use aqueous systems containing at least one pound oftotal inorganic salts per gallon of water, and preferably greater thanabout a pound and a quarter per gallon. Upper limit of concentrationwill, of course, be the limit of solubility of the salts in the aqueoussystem.

The improved results achieved by the aqueous compositions of theinvention stem from the particular ratio of the particular ammoniumsalts employed. It is, in fact, well known in the art to employ ammoniumphosphate and ammonium sulfate either alone or in combination with oneanother and with other components in fire retardant formulations, Ingeneral, however, such formulations have been dry, as exemplified bysuch U.S. patents as the following:

Reiss, U.S. 2,881,138, issued Apr. 7, 1959 Steppe et al., U.S.3,017,348, issued Jan. 16, 1962 Cawood, U.S. 3,063,940

Simes, U.S. 3,179,588

Such dry formulations, however, present little or no corrosion problem.Aqueous systems containing various ammonium salts in various ratios aretaught by such U.S. patents as that to Schuler, U.S. 502,867, issuedAug. 8, 1893.

AMMONIUM SALTS The reduced corrosivity of the compositions of the intionare achieved by aqueous gels comprising diammonium phosphate (NH HPO andammonium sulfate in a particular weight ratio. That ratio lies from 1part of the sulfate to 1 part of the phosphate, to 5 parts of thesulfate to 1 part of the phosphate. The aqueous gels of the inventionhaving this ratio of ammonium sulfate to diammonium phosphate arecharacterized by a pH of between 6.5 and 7.5, and by substantiallyreduced corrosivity toward structural pump, tank and aircraft metals.Particularly, reduced corrosivity is exemplified by the aqueous gelwherein the sulfate to phosphate ratio lies from about three parts ofammonium sulfate to one part of diammonium phosphate, to that having aratio of five parts of ammonium sulfate to one part of ammoniumphosphate.

pH CONTROL One important feature of the aqueous compositions of theinvention is the range of hydrogen ion concentration therein. Bymaintaining the hydrogen ion concentration, herein identifiedconventionally by the pH notation, within specified limits, thecorrosivity of the ammonium salt formations is materially reduced.

Such reduction in corrosivity is achieved by maintaining the pH of theaqueous diammonium phosphate compositions of the invention between about6.5 and about 7.5. This maintenance of pH is accomplished by includingin the aqueous diammonium phosphate composition only a specified amountof ammonium sulfate. Such pH control is achieved by employing theammonium sulfate in a weight ratio of from about 1:1, based on thediammonium phosphate, to about :1 on the same basis. The pH ofrepresentative aqueous compositions of diammonium phosphate and ammoniumsulfate is shown in the following Table I. The compositions tabulatedhave a concentration of one pound of total ammonium salts per gallon ofwater, and also contain sufiicient carboxymethyl cellulose to give aviscosity of 1000 cp., Rhodamine B dye, and both benzotriazole andsodium fluosilioate corrosion inhibitors.

TABLE I Weight ratio, diammonium phosphate to ammonium sulfate: pH(NH4)2SO4 3.10116 1:5 7.0

1:1 7.4 (NH4)2HPO4 alone 7.7

VISCOSITY In aerial firefighting, unthickened solutions of ammoniumsalts in water have been found to be relatively ineifective. Whendropped from aircraft, such solutions tend to TABLE II Wt. Ratio, (N H4)2HP0 Metal Thimo, (NH4)2HPO4 (NI-102804 Aluminum 0-24 1.96

pH of solution 7. 7 7. 4 7. 0 7. 0

Substantially less attack on the aluminum was made by the compositionsof the invention than by diammonium phosphate alone.

The compositions heretofore described display substantially reducedcorrosivity toward copper, aluminum and other structural metals.However, by including benzotriazole in the compositions to at leastabout 0.1% w., based on the total ammonium salts, and preferably betweenabout 0.1% w.-1.0 w. on the same basis, a surprising further reductionin corrosivity was achieved.

BENZOTRIAZOLE In Table III are presented data showing the effect ofadding small amounts of benzotriazole to the diammonium phosphate/ammonium sulfate compositions of the invention. Set forth in the tableare the penetrations, in mils/yr. of the test metal, of various aqueoussystems having a concentration of about 1 pound of total ammonium saltsper gallon of water. Where benzotriazole was employed, it was used at aconcentration of 0.21% w. or 0.42% w., based on the total salts. Thetest solutions contained sufficient carboxymethyl cellulose to give eacha viscosity of 1000 cp. In the table, benzotriazole is abbreviated asbz. for compactness.

TABLE III (NHa 22HP04 Weight Ratio (NH4)2HPO4/(NH4)2SO4 one Metal lame,1:1 1:3 1:5

w/o 0.42% w. w/o 0.21% w. 0.42% w. w/o 0.21% w. 0.42% w. w/o 0.21% w.0.42% w. bz. bz. bz. bz. bz. bz. bz. bz. bp. bz. 2.

Copper 024 43. 7 7. 7 26.3 1.5 18.1 8.8 1.7

24-48 50.1 16.4 29.5 5.9 22.4 8.5 3.2 12 7 6.0 0 6 72-96 19 8 7.9 1 0 pHof solution 7 7 7 7 7.4 7 4 7 4 7 0 7.0 7 0 drain rapidly off foliage,to splash off intended targets, and to be quickly absorbed by soil.Accordingly, it is necessary to thicken the solution to a consistencysuch that it will adhere to targets and thus protect them.

It has been found that a viscosity of at least one thousand centipoisesis required for the gels of the invention to achieve these desirableresults. Such a viscosity is achieved by gelling the ammonium saltsolutions of the invention with a water-miscible thickener or gellingagent. Exemplary of such thickeners are carboxymethyl cellulose, suchpolypectates as ammonium polypectate and sodium polypectate, algin, andsuch algin salts as sodium alginate, some clays such as bentonite andatt-apulgite, various gelatins, anhydrous silica, starch, and varioussoaps. Of these thickeners, carboxymethyl cellulose combines thedesirable properties of relatively low cost with substantial thickeningpower, and is the preferred thickener. While the concentration of thethickener will depend both on its nature and on the nature of the systemin which it is employed, the thickener employed in the formulations ofthe invention will be used at a concentration such that the resultingcomposition will have a viscosity of at least one thousand centipoises,and preferably from twelve hundred to eighteen hundred centipoises. Ingeneral, at least about 5% w. of the thickener gives sufficientviscosity to the gels.

The reduced corrosivity of the formulations of the invention towardaluminum is illustrated in the following Table II. In the table,penetration in mils/yr. of aluminum by various solutions containing onepound of ammonium salts per gallon of water is shown. Each solution wasthickened with carboxymethyl cellulose to a viscosity of 1000 cp.

The inclusion of the benzotriazole dramatically reduced the corrosion ofthe test metals.

SODIUM FLUOSILICATE In use, the gel formulations of the invention becomedeposited not only on the copper and bronze elements of aircraft butalso on the aluminum fuselage. It is therefore desirable that theformulations display reduced corrosivity to aluminum and its alloys.While the particular aqueous diammonium phosphate/ ammonium sulfate gelsof the invention are substantially less corrosive toward such metalsthan are other ammonium salt solutions, their corrosivity can be furtherreduced by inclusion of a stabilizing amount of sodium fluosilicate.Thus, it has been found that inclusion of between about 0.1% w. to about1.0% w. of sodium fluosilicate, based on the ammonium salts, iseifective to impart to the gels of the invention a reduced corrosivitytoward aluminum and aluminum alloys.

To illustrate the corrosion-reducing properties imparted by the sodiumfluosilicate to the ammonium sulfate/diammonium phosphate gelcompositions of the invention, the fol-lowing Table IV is presented. Inthe tests described therein, the test solutions had the followingcomposition:

Diammonium phosphate/ ammonium sulfate As specified. Carboxymethylcellulose 9.010% by weight, based on total weight. Rhodamine B pigment.05 by weight, based on total weight. Sodium fluosilicate .84l% byweight, based on total weight.

The tests were performed at room temperature with partially immersedcoupons of the metals specified. Corrosion attack on the coupons is setforth as penetration in mils per year.

TABLE IV.-OORROSION OF METAL Not only is sodium fiuosilicate effectiveto reduce the corrosivity of the ammonium salt solution of theinvention, but it also serves, surprisingly, to stabilize the systemitself against biological degradation. The gelling agents of theinvention are, to the extent that they are organic in nature, subject tobacterial attack. Upon bacterial infection of the system, the molecularweight of the gelling agent becomes reduced and the viscosity of thesystem decreases rapidly. Presence of the sodium fluosilicate serves toprevent such microbial degradation and thus preserve the viscosity ofthe gel during storage.

One advantage of the fire-retardant aqueous diammoniumphosphate/ammonium sulfate compositions of the invention is theireffectiveness as residual fertilizers. Not only do they serve to limitthe spread of forest fires but, once washed off trees and branches ontothe soil, they serve as readily-available sources of plant nutrientnitrogen, phosphorus and sulfur. The compositions thus have theadvantage of stimulating regrowth of grass, bushes and trees inburned-over areas and thus assisting in reforestation. Such growth alsostabilizes the soil in water sheds and retards the washing away of soilfrom burnedover areas.

MARKING AGENT To assist aircraft pilots in following the dropping oftheir loads, it is desirable to include in the compositions of theinvention a small amount of marker dye or pigment. The dye serves toshow the location and extent of coverage of the fire-retardantcomposition on the target area. A wide variety of dyes are available forthis purpose, in all colors and hues. Both fluorescent andnonfluorescent dyes may be used. Naturally, a dye or pigment should beselected whose color gives maximum contrast against the target grass orfoliage; such colors as yellows, oranges, and reds are preferred togreens, blues and browns. The amount of dye or pigment employed will, ofcourse, depend on the intensity of color any particular coloring agentimparts to the fire-retardant composition. A visible amount of themarking agent will be required; in general, at least about 0.001% w. ofmost dyes and pigments has been found to be sufficient, while use ofmore than about 1.0% w. appears unnecessary.

Representative dyes that may be employed as marking agents in thecompositions of the invention are those dyes shown in the Colour Indexof the Society of Dyers and Colourists. Typical dyes include Rhodamine B(hydrochloride of diethyl m-amino-phenolphthalein) red, fluorescent AzoRed A (sodium salt of 4-sulfo-a-naphthaleneazo-anaphthol-3,6-disulfonicacid) red Naphthol Orange (sodium salt ofp-sulfobenzene-azo-achloro-m-phenylene-diamine-sulfonic acid) yellowNaphthol Orange (sodium salt of p-sulfobenzene-azo-unaphthol) orange-redWhile coloring agents such as dyes or pigments may be either soluble orinsoluble in the aqueous compositions of the invention, water-solubledyes are preferred since they are more readily formulated with thecompositions described, can be more uniformly distributed throughout thegel formulation, and do not settle out on storage.

FORMULATION AND USE The compositions of the invention can be readilyformulated with methods well known in the art. They may be loaded intoaircraft tanks and dropped onto fires or fire-threatened areas withconventional equipment and by using conventional methods. They may bedropped from either fixed-wing or helicopter aircraft from anyconvenient height and in any desired amount.

The compositions of the invention are characterized by importantadvantages over the aqueous fire-fighting compositions of the art.Unlike borate compositions, which are toxic to some varieties of treesand plants, the ammonium salt compositions are actually beneficial toforest and rangeland. The compositions are substantially less corrosiveto aircraft, storage tank and pumping equipment than the aqueousdiammonium phosphate retardant compositions known to the art.Furthermore, they are economical, readily prepared from availablechemical materials, and have been found to be highly effective in forestfire control.

To illustrate the nature of the formulations of the invention, thefollowing typical compositions are set forth. It should be understood,however, that these examples are illustrative only and are not to beregarded as limitations to the appended claims since the basic teachingsthereof may be varied at will as will be understood by one skilled inthe art. In the examples, the proportions are expressed in parts byweight unless otherwise indicated.

FORMULATION I [1:1 Wt. ratio (NR4) 2HP O4/(NH )2SO Dry Component Percentw. Pounds/Ton Diammonium Phosphate 45. 052 901. 0 Ammonium Sulfate- 45.052 901.0 Carboxymethyl Cellulose 9.010 0 Sodium Fluosilicate 0. 84117.0 Rhodamine B Dye 0.05 1.0

Dry Component Percent w. Pounds/Ton Diammonium Phosphate 22. 525 450. 5Ammonium Sulfate 67. 525 1,351 5 Ammonium Polypectate 9.010 180. 0Sodium Fluosilieate 0. 425 8. 5 Benzotriazole 0 425 8.5 Rhodamine B Dye0.05 1.0

This formulation, when made up into a solution having a concentration of1 pound of ammonium salts per gallon of water, has properties comparableto those of Formulation I; save that its pH is about 7.0.

FORMULATION III [1:5 Wt. ratio (NI-IOzI-IPOq/(NHOrSOd Dry ComponentsPercent w. Pounds/Ton Diammoniurn Phosphate 15.017 300.0 AmmoniumSulfate.. 75. 087 1, 502v 0 Carboxymethyl Cellulose. 0. 010 180 0 SodiumFluosilicate 0. 841 17.0 Rhodamine B Dye 0 05 1 0 This formulation wasmixed with water to a concentration of one pound of ammonium salts pergallon of Water.

The resulting mixture was a red solution having a vis' cosity of about1000 centipoises and a pH of about 7.0.

Where dimensions of viscosity of the formulations of the invention aregiven, the measurement thereof was made with a Brookfield viscometer,using a N0. 3 spindle 30 r.p.m., and applying a multiplication factor of40 to the reading on the scale of 100.

When any of these formulations is dropped on grass or foliage in frontof a forest fire, the formulation adheres to the grass or foliagewithout material drainage or runoff. The resulting protected area charsin the heat, but does not flame, and effectively prevents the furtherspread of the fire therethrough. Location and extent of the protectedarea is shown in red by the presence in the system of the dye.

I claim as my invention:

1. A fire-retardant composition consisting essentially of (a) water,

(b) a water-miscible thickener, and

(c) dissolved diammonium phosphate and ammonium sulfate; the weightratio of said diammonium phosphate to said ammonium sulfate being fromabout 1:1 to about 1:5; and said fire-retardant composition having aviscosity of at least 1000 centipoises and a pH of between about 6.5 andabout 7.5.

2. The fire retardant composition of claim 1 wherein the composition hasfrom 0.1% w. to 1.0% w. of sodium fluosilicate.

3. The fire retardant composition of claim 1 wherein the composition hasfrom 0.1% w. to 1.0% w. benzotriazole.

4. The fire retardant composition of claim 1 having at least 5% w. ofcarboxymethyl cellulose as said thickener; and wherein the weight ratioof diammonium phosphate to ammonium sulfate is from about 1:3 to about1:5.

5. The fire-retardant composition of claim 4 wherein the composition hasa concentration of diammonium phosphate plus ammonium sulfate of atleast one pound per gallon of water; from 0.1% W. to 1.0% W. sodiumfluosilicate, and from 0.1% w. to 1.0% w. benzotriazole.

6. The fire retardant composition of claim 4 wherein the composition hasa visible amount of colored marking agent.

7. The method of fighting forest fires, comprising depositing from anaircraft onto an area adjacent a forest fire the composition of claim 1.

8. The method of fighting forest fire, comprising the aerial depositionof the composition of claim 5 onto an area adjacent a forest fire.

9. The fire-retardant composition of claim 1 wherein the weight ratio ofdiammonium phosphate to ammonium sulfate is from about 1:3 to about 1:5.

10. The fire-retardant composition of claim 1 wherein said thickener isselected from the group consisting of carboxymethyl cellulose, ammoniumpolypectate, sodium polypectate, algin, sodium alginate, bentonite,attapulgite, gelatin, anhydrous silica, starch and soap.

References Cited UNITED STATES PATENTS 2,941,953 6/ 1960 Hatch 252-3893,196,108 7/1965 Nelson 2528.1 XR 3,249,534 5/1966 Ware 252-8.13,293,189 12/1966 Morgenthaler 252--2 3,334,045 8/1967 Nelson 2522FOREIGN PATENTS 945,702 1/ 1964 Great Britain.

OTHER REFERENCES Chemical Week, Oct. 7, 1961, pp. 39, 40. C. & E. N.,July 17, 1961, pp. 35, 36.

MAYER WEINBLATT, Primary Examiner.

